Quote:-Is there a difference between the 2 methods: add(JaObject ob) and draw(JaObject jo), which seem to have the same effect (adding a JaObject in the frame)? See the example below.

the design goal of the method "add()" is to add objects to the list of objects without drawing them.
One can draw all objects at once after calling the "update". This should speed up the code in case of many objects. The method "draw" adds an object to the list and calls "update()". At least, this is the way how it works for HPlot. It is possible that canvas resizing with the mouse also triggers canvas update in case HPlotJa.